The present invention relates to continuous casting, more particularly to detection of any abnormality occurring in a casting metal, such as steel flowing through a mold used for continuous casting.
The productivity, safety and maintenance of continuous casting equipment are largely effected by the occurrence of abnormalities, such as a so-called "breakout" which occurs, in a first case, when an opening is formed in a coagulated shell, the solidified shell of the casting liquid metal, (hereinafter referred to as shell, for brevity) of the molten steel in the mold and/or, in a second case, when a large-size impurity particle, made of nonmetal, appears close to the surface of the shell.
According to the conventional art, the temperature is determined, at the shell surface, where the shell has just been drawn out from the mold. If the detected temperature is extremely high, then it is very likely that a breakout may take place during the continuous casting. Therefore, the portion, where the breakout is most likely to occur, is quickly cooled down so as to prevent such a breakout from occurring. However, it is difficult to prevent all such breakouts from occurring. That is, there still exists the possibility that, although the above-mentioned operation for cooling down the temperature is conducted, a breakout may still occur in some portion of the shell. The reason for this is believed to be that, since the temperature is detected at the shell surface which has been drawn out from the mold and the operation for cooling down is applied to suspected areas, it is already too late to prevent a breakout from occurring. Further, it is almost impossible, to prevent the occurrence of a breakout, due to the presence of the large-size particles of the impurity, which is a nonmetal. This is because it is impossible to detect such an impurity particle, appearing near the shell surface, flowing right beneath the surface of the mold, and, accordingly, there has been no method for preventing the occurrence of a breakout.
Contrary to the above, if it is possible to detect an abnormality, which will induce the breakout, when the abnormality is still located inside the mold, then such breakout could be prevented from occurring by the following method. That is, the continuous casting speed could be made considerably slower than usual or the casting could be stopped for a while, so that the molten steel could be sufficiently cooled down and thereby allowed to form a shell having a thickness sufficient to prevent the occurrence of a breakout.
As part of the conventional art, two specific references have been known, i.e., publications of Japanese patent application laid open Nos. 51(1976)-151624 published Dec. 27, 1976 and 55(1980)-84259 published June 25, 1980, respectively. However, as will be mentioned in detail hereinafter, the methods disclosed in these publications have common shortcomings in that, firstly, the methods have no capability for detecting an opening in the shell, which opening is produced when the shell is partially stuck to the inside wall of the mold, and, secondly, the methods are liable to erroneously detect a pseudo opening, that is the detection is not performed with a high degree of accuracy.